1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to managing hyper frame number (HFN) de-synchronization in radio link control (RLC) unacknowledged mode (UM).
2. Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
In W-CDMA, RLC unacknowledged mode (UM) is a radio link protocol in which a success or failure of the received protocol data units (PDUs) are not acknowledged. RLC UM may be used for real-time or near-real-time applications as well as delay-sensitive applications. In RLC UM, ciphering and deciphering are performed on transmitted packets by utilizing a time-varying parameter value or count referred to as COUNT-C, which is a combination of a short sequence number (SN) and a long SN. The short SN is a 7-bit RLC SN that is part of the RLC UM protocol data unit (PDU) header. The long SN is a 25-bit RLC UM HFN that is incremented at each RLC SN cycle. Accordingly, upon transmitting every 127 consecutive RLC UM PDUs, an RLC SN cycle at the transmitting RLC UM entity is completed, the RLC SN at the transmitting RLC UM entity wraps around, and the HFN at the transmitting RLC UM entity is incremented. Meanwhile, if the receiving RLC UM entity misses more than 127 consecutive PDUs, because the receiving RLC UM entity is not aware of the missed PDUs, the HFN at the receiving RLC UM entity is not incremented, resulting in a de-synchronization between the HFNs at the transmitting and receiving RLC UM entities. Thereafter, if further RLC UM PDUs are transmitted and received correctly, due to the de-synchronization between the HFNs at the transmitting and receiving RLC UM entities, the data in the received RLC UM PDUs will be erroneously deciphered at the receiving RLC UM entity, and since the transmitting and receiving RLC UM entities will not be able to detect such error, the corrupted PDUs will just be forwarded to higher layers. Accordingly, in RLC UM, HFN de-synchronization can result in incorrect service data unit (SDU) generation or garbled voice in, e.g., voice over HSPA applications.
As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. Thus, in this case, improved apparatus and methods are desired for managing HFN de-synchronization in RLC UM.